1. Field of the Invention
The present invention is broadly concerned with an apparatus and method for locating and marking regions of obstruction in the upper airway of a patient. More particularly, it is concerned with a multiluminate catheter having an outer wall circumscribed by a plurality of discrete perforate regions. Each lumen is coupled at one end with one of the perforate regions, and at the other end with a pressure transducer for measuring pressure changes in the lumen which indicate the presence of a region of obstruction. Each lumen is equipped with a syringe port for injecting a dye marker through the lumen and outwardly through the perforate region and into the obstructed regions, and the outer catheter wall includes a radiopaque marker for determining the placement of the catheter in situ.
2. Description of the Related Art
Obstructive Sleep Apnea Syndrome, (OSA Syndrome) is a respiratory disorder characterized by periodic cessation of breathing caused by upper airway obstruction. The primary consequences of OSA Syndrome are episodic asphyxia and sleep fragmentation. More than 30,000 patients seek treatment for OSA Syndrome each year. The most common clinical features of the syndrome are heavy snoring and daytime sleepiness. OSA Syndrome is a serious disorder and its consequences can be life-shortening. An association has been demonstrated between sleep apnea and increased risk of hypertension, myocardial infarction and stroke.
The etiology of the syndrome is obstruction of one or more portions of the upper airway. Sleep causes the muscles of the upper airway to relax and the associated soft tissues to sag, resulting in narrowing or collapse of the upper airway, and consequent reduction in ventilation. Although the diaphragm continues to contract and the contractions may even intensify, obstructive apnea may be observed in sleep studies as a cessation of the airflow at the nose and mouth.
The decreased ventilation causes a rise in carbon dioxide tension and a drop in oxygen saturation of the arterial blood. The entire body is affected, since oxygen delivery to the tissues may be reduced by as much as 60% during an episode of OSA.
A diagnosis of OSA syndrome is generally established through a polysomnographic study in a sleep laboratory. Such studies may include monitoring of brain activity by electroencephalography (EEG), eye movement by electrooculography, cardiac rhythm by electrocardiography, blood oxygen level by oximetry, airflow measurement at the nose and mouth, and measurement of inspiratory effort by inductance plethysmography, intraesophageal pressure measurement or surface electronmyography of the inspiratory muscles. The upper airway should be evaluated for structural problems as well, such as nasal polyposis, lymphomatous involvement of the nasopharynx, nasopharyngeal carcinomas and bone abnormalities.
Once obstructive sleep apnea syndrome is diagnosed, therapy includes correction of associated medical conditions, drug therapy and dietary management, mechanical aids and surgical intervention. Correction of the associated medical conditions may be aimed at the effects such as excessive daytime sleepiness or the consequences, such as right-sided heart failure. Such therapy is specific to the individual, and generally does not address the underlying causes of the apnea. In certain cases avoidance of provoking agents such as alcohol, sedatives and androgens may be effective. Where obesity is contributory, dietary management or gastric stapling may be employed to achieve sustained weight loss. Drug therapy has been shown to be of only limited effectiveness in treating OSA.
Mechanical aids, such as Continuous Positive Airway Pressure (CPAP) and Bilevel Positive Airway Pressure (BiPAP) are the most commonly employed therapy for management of obstructive sleep apnea. Nasal CPAP treatment involves placing a mask over the nose for use as a pneumatic splint, while a stream of air is pumped through the mask and into the patient's airway. BiPAP treatment involves additional independent programming of the inspiratory and expiratory pressures, so that the pressure is lowered during exhalation. Such devices may be extremely effective when used correctly and regularly. However, because they do not correct the underlying causes of obstructive sleep apnea, they must be used indefinitely.
Mechanical aids are also subject to poor patient compliance. About forty percent of patients are estimated to experience difficulty tolerating CPAP for prolonged periods of time. One of the problems associated with nasal CPAP is the bulk of the required equipment. Patient complaints include that the equipment comes off during sleep, that it causes dryness of the mucous membranes of the mouth and throat, and that it makes noise which keeps the sleeper or spouse awake.
Surgical therapy may be employed to improve airway patency through permanent alteration of the soft tissues. Surgical therapy is particularly effective where the obstruction is caused by uvulopalatal narrowing of the relaxed pharyngeal airway. The most commonly practiced procedures are palatal surgery such as uvulopalatopharyngoplasty (UPPP) and laser-assisted uvulopalatoplasty (LAUP), in which the tonsils, uvula, and portions of the soft palate and posterior pillars of the fauces are excised in order to widen the posterior pharynx behind the palate.
Despite the extensive nature of such surgical procedures, UPPP and LAUP are not effective in curing obstructive sleep apnea in about half of all cases. Other surgical procedures, such as nasal surgery, genioglossus tongue advancement, hyoid suspension, maxillomandibular advancement and tracheotomy are also available, and may be attempted when UPPP and LAUP have failed.
In order to make a differential diagnosis of OSA, to identify whether a patient may be a candidate for surgical therapy, and to determine the appropriate surgical procedure in the first instance, it is thus necessary to precisely identify the tissue region which causes narrowing or occlusion of the airway when the patient is at rest.
In the past, various attempts have been made to employ catheters to identify such areas within the upper airway. Such devices employ a flexible cannula, such as an endotracheal tube having an aperture at or near the end, coupled with an external pressure transducer. The catheter is inserted through one of the nares into the upper airway of a patient. When occlusion occurs, a drop in pressure is relayed by the transducer to a visual display. While such catheters may be employed to verify the existence of an occlusion somewhere within the airway, they do not serve to identify the location of the obstruction.
By using a pair of catheters to measure respiratory pressure and by gradually withdrawing one of the catheters until a pressure drop is registered, it is possible to identify the general area of a single region of occlusion. Graduated markings have been applied along the length of the catheter as an aid in approximating the location of an obstruction within the patient. However, occlusions which are caused or exacerbated by relaxation of the upper airway in OSA syndrome must be evaluated in a sleeping patient through polysomnography. The necessary manipulation of two catheters required by such methods renders them unsuitable for use during sleep apnea studies. In addition, identification of multiple regions of occlusion would require extensive catheter manipulation, which is likely to cause abrasion of the soft tissues of the upper airway and result in patient discomfort.
Attempts have been made to locate airway obstructions with a multiluminate catheter in which each lumen is coupled with an opening in the side of the catheter. However, such devices contain only a single opening in the catheter wall coupled with each lumen. These individual openings are subject to clogging by airway secretions, which may cause a false low pressure reading. Because of the length of the airway and limitation on the number of possible lumens by the catheter diameter, external catheter openings must be widely placed. Thus, even where the openings remain unclogged, they are unable to particularize the location of an obstructed region.
The apparatus and method of the present invention are specifically designed to employ during a sleep apnea study a single, stationary catheter to locate with particularity regions of obstruction in the airway of a patient. The obstructing tissue is then marked for surgical removal or reduction.